Biomass harvesting shows minimal impact on soil

Iowa State University and USDA-ARS researchers continue to find that removing corn stover at the rate recommended by POET-DSM is sustainable.

Recent data continue to demonstrate that harvesting crop residue can be a responsible part of good farm management, reports Project LIBERTY, Emmetsburg, Iowa. Project LIBERTY will use corncobs and stover when its cellulosic ethanol plant begins producing cellulosic ethanol (expected in 2013). For the last four years, it has commissioned soil sustainability work from researchers at Iowa State University and the USDA.

Stuart Birrell, Iowa State University (ISU), and Douglas Karlen, USDA-ARS, led the research. They found that at the removal level that POET-DSM (the 50/50 joint venture) recommends, there is no reduction in yield, and removal rates are well within the sustainability limits.

POET-DSM contracts for about one ton of biomass per acre with participating farmers, which is less than 25 percent of the available aboveground biomass, the company reports. They are contracting for 85,000 tons this year. Project LIBERTY will require about 285,000 tons per year once cellulosic ethanol production gets under way.

“From the beginning we’ve said we would pay close attention to the data in determining our contracts with farmers,” said Larry Ward, senior vice president, Project Development, POET. “We’re clearly well within the limits of what the research says is responsible biomass harvesting.”

ISU’s Birrell said nutrient replacement is minimal, with no evidence of a need to replace nitrogen. Based on the research, POET-DSM recommends the addition of 10 to 15 pounds of potash when soil tests indicate it is needed. “The natural soil fertility and understanding of that fertility is far more important and has a greater effect on fertilizer recommendation rates than the relatively small amounts you’re taking off in stover harvesting,” Birrell said.

ISU and USDA-ARS also have studied six harvest methods to provide area farmers with data about biomass. The effects of biomass harvesting on soil carbon have proven to be minimal according to measurements of soil organic carbon.